What it does:Attempts to save space by storing frame data in the smallest possible frame. Usually MP3s are already stored in the most efficient way possible. However, for high-bitrate CBR files (like --preset insane) there can be a lot of wasted space

psyllium has made a great Windows GUI for this program. The GUI thread is here. Many people will find it easier to use than the CLI, and it has a few more features too (recursive directory support, 2-pass CBR).

Features:* Can make --preset insane files up to 10% smaller LOSSLESSLY (depending on the LAME version used)* Squeezes out all the padding it can from any MP3 (Will not produce a larger file, unless you use the -b switch or something goes wrong)* Writes valid LAME/XING header for proper VBR seeking* Many people also use this backwards, to losslessly turn VBR into larger CBR files to humor players which can't handle VBR* Includes a brute-force compression optimization option as of 1.10 to further compress files* Now supports Unicode file names and paths* Support for encoding an entire directory of files* Works on Windows, Linux, 64-bit Linux, Linux through WINE, and should work perfectly on any other platform with an OCaml port* GPL, so anybody can tweak it as long as it stays GPL

A few caveats:* The program will always output an MP3 that doesn't use CRCs, even if the input file uses CRC. This is primarily laziness on my part, but nobody really needs them, and it saves 600 bits per second... (it's a feature, not a bug!)* The 32-bit version will not process files larger than 1GB. The 64-bit version has a much higher limitation (4EB) which is unlikely to be encountered.* There seems to be an incompatibility with the multi-threaded repacking code and 32-bit Windows XP. If you run across an error, try adding "--workers 0" to the command line.